Protein kinases play important roles in promoting or retarding transitions between different stages and checkpoints of the cell cycle. In humans, a closely related subgroup of three serine/threonine protein kinases (the Aurora kinases), are believed to play a key role in protein phosphorylation events that regulate the mitotic phase of the cell cycle. The Aurora kinases are overexpressed in several types of human cancer cells such as colon, breast, and other solid tumors. Aurora A and Aurora B genes are amplified in breast and colorectal cancers, while the Aurora C gene is located in a region that is rearranged or deleted in several cancer cells. Overexpression of Aurora A in rodent fibroblasts induces transformation, indicating that Aurora A is oncogenic. Aurora A mRNA expression has been linked to chromosomal instability in human breast cancers. Thus, there is a need for compounds that inhibit any or all of the Aurora kinases in the treatment of cancer and other proliferative disorders.